1. Field of the Invention
The present invention relates to a ceiling electrode plate and a substrate processing apparatus, and more particularly, to a ceiling electrode plate provided to face a substrate holding stage by interposing a process space therebetween.
2. Description of the Related Art
A substrate processing apparatus, which performs an etching process on a wafer serving as a substrate, includes a chamber that accommodates the wafer and may be depressurized, a substrate holding stage that is provided inside the chamber and on which the wafer is placed, and a ceiling electrode plate (CEL) provided to face the substrate holding stage by interposing a process space therebetween. Plasma is generated in the depressurized chamber, and the plasma is used to etch the wafer. The ceiling electrode plate is supported by an electrode supporting unit (UEL) by interposing a cooling plate that serves as a heat diffusion plate.
When a plasma process, for example, an etching process, is performed on the wafer, an etching rate (E/R) of each portion of the wafer is influenced by a temperature of each portion, and thus there is a need to uniformly maintain surface temperatures of elements provided inside the chamber, for example, the wafer, the substrate holding stage, the ceiling electrode plate, etc., during the etching process. However, since the inside of the chamber is held in a vacuum state, it is difficult to transfer heat between the elements provided inside the chamber, and it takes time to stabilize temperatures of the elements.
Also, during the etching process of the wafer, heat generated from plasma is applied to the ceiling electrode plate provided over the substrate holding stage on which the wafer is placed, and a temperature of the ceiling electrode plate is changed. The temperature of the ceiling electrode plate affects distribution of radicals included in the plasma of the process space, and thus if the temperature of the ceiling electrode plate is changed while a plurality of the wafers in the same lot are processed, it is difficult to uniformly perform an etching process on the plurality of wafers in the same lot. Accordingly, a coolant passage, through which a coolant including, for example, a cooling water, flows, is provided as a temperature adjusting mechanism in the electrode support that supports the ceiling electrode plate. Thus, the ceiling electrode plate is cooled via the cooling plate that serves as a heat diffusion plate, thereby adjusting the temperature of the ceiling electrode plate that is directly influenced by heat generated from the plasma.
However, adhesion strengths of a contact surface between the ceiling electrode plate and the cooling plate and a contact surface between the cooling plate and the electrode support are not so high, and heat transfer efficiency therebetween is low due to the vacuum atmosphere. Accordingly, a time lag occurs in controlling the temperature of the ceiling electrode plate, and thus it is difficult to adjust the temperature of the ceiling electrode plate to a desired temperature from when generation of the plasma begins, thereby causing instability of a process property such as etching rates of wafers.
On the other hand, a temperature adjusting technology for improving heat transfer efficiency between elements of a plasma processing apparatus has been recently developed by the present applicant (refer to, for example, Patent Reference 1). In this technology, a heat transfer sheet is provided between the elements of the plasma processing apparatus, for example, between a focus ring and a susceptor, to improve heat transfer efficiency.
However, an applicable technology of the above-described heat transfer sheet has not necessarily been established, and particularly, a technology that is applicable to a ceiling electrode plate, which is heated by directly receiving heat generated from plasma, has not been sufficiently established.
3. Prior Art Reference
(Patent Reference 1) Japanese Patent Laid-Open Publication No. 2002-016126